Carbonation process for purifying sugar juice



June 30, 1942.

L/M/NG REAGENT- A. R. NEES ETAL CARBONATION PROCESS FOR PURIFYING SUGAR JUICE Filed July 50. 1940 AL PHEUS #2 2 ATTORNEYS CARBON DIOXIDE 695 NETT FORD

Patented June 30, 1942 CARBONATION PROCESS FOR PURIFYING SUGAR JUICE Alpheus R. Nees, Arthur N. Bennett, and Edwin H. Hungerford, Denver, 0010., assignors to The Great Western Sugar Company,

Denver, 0010.,

a corporation of New Jersey Application July 30, 1940, Serial No. 348,568

(Cl. l2759) 7 Claims.

This invention relates to new and useful improvements in the purification of beet sugar juice, and particularly to a new carbonation process which effects the desired purification of the juice while avoiding the formation of excessive foam or froth.

In the purification of beet sugar juice, the general prOcedure is to add to raw juice an alkaline reagent such as milk of lime or calcium saccharate, allow the reagent to react with nonsugars in the juice, and then convert the excess of lime into insoluble calcium carbonate by passing carbon dioxide gas through the mixture. This process is known as carbonation. In the past it has usually been carried out in batches. More recently a valuable continuous carbonation process has been adopted pursuant to the invention claimed in United States Letters Patent No. 2,164,186.

During the carbonation of beet sugar juice more or less foam or froth is formed which very often causes serious difiiculties in sugar factory operations. When excessive foaming occurs the volume of juice undergoing treatment increases many fold, so that relatively large tanks having foam vents and return pipes must be provided to allow escape of the foam and return thereof into the process. In addition to this difiiculty, the efficiency of carbon dioxide absorption is reduced by foaming, tion becomes slower and sometimes seriously limits the capacity of the carbonation station. At its Worst, the foam is a stiff, very stable, semisolid emulsion which greatly hampers the juice purification and requires considerable special attention and treatment.

Heretofore the problem of excessive foaming or frothing has been combatted by the addition of oil or other reagents which cause the bubbles to break or inhibit their formation. Such methods of combatting foam are objectionable because they add expense and complicate the process of juice purification, and in any event they serve only to reduce difficulties rather than to eliminate the source of trouble.

An object of this invention is to provide a new and useful process of carbonation by which the formation of excessive foam or froth and the difliculties resulting therefrom may be avoided. Anotherobject is to eliminate the necessity of adding oil or other anti-foam reagents to the sugar juice during carbonation. A further ob ject of this invention is to provide an improved method of carrying out the aforesaid continuous carbonation process, whereby to avoid excessive so that the rate of carbonafoaming or frothing during the gassing of the juice with carbon dioxide.

We have found that the formation of excessive foam or froth during the carbonation of beet sugar juice is related to a transient condition of alkalinity in the juice, and that there is a certain range of alkalinity for any juice in which excessive foaming is likely to take place during carbonation regardless of the character of the juice, the amount of liming reagent employed or the temperature of the juice. We have also found that excessive foaming or frothing can be avoided by keeping the alkalinity of the juice outside of this active foaming range during the gassing with carbon dioxide. These findings are utilized according to our invention to provide a new and improved carbonation process which effects the desired purification of the juice without encountering excessive foam formation and without requiring the use of anti-foam reagents for satisfactory process operation.

When carbonating according to prior processes, for example, the sugar juice is treated with liming reagent until it is saturated with dissolved lime and contains an excess of undissolved lime, and the limed juice is then treated with carbon dioxide to precipitate lime as calcium carbonate and reduce the alkalinity of the juice to a satisfactory point for filtration. In the early stage of gassing the excess of undissolved lime goes into solution substantially as rapidly as dissolved lime is converted into calcium carbonate, so that the juice remains substantially saturated until the excess of lime is exhausted. During this stage of the process it has been found that there is little or no objectionable foam formation. Excessive foaming begins, however, as soon as the continued gassing has caused the alkalinity of the juice to drop slightly below the saturation point, and such foaming has been found to continue until the alkalinity has been reduced to a point equivalent to about 0.11 to 0.20 gram CaO per cc. of juice, depending upon qualities of the juice. Thereupon excessive foaming ceases, and the mixture becomes fluid and remains o as the end point of carbonation, e. g. an alkalinity of 0.06 to 0.88 gram CaO per 100 cc., is reached.

In accordance with the present invention, the carbonation of beet sugar juice is carried out by treating the juice with an excess of liming reand then precipitating the lime as calcium carbonate, but the liming reagent and the carbon dioxide are introduced under such control that the alkalinity of the juice is always kept outside of the critical foaming range of the juice in question. More specifically, the juice is at least saturated with liming reagent, and it is then carbonated to the desired end point in stages so that its alkalinity during carbonation never attains a value within the range between a point slightly below the point of saturation and a lower limit, depending on the nature of the juice, of for example about 0.20 gram CaO per 100 cc. of juice.

The alkalinity of beet sugar juice corresponding to the point of saturation with liming reagent is usually about 0.40 to 0.60 gram of CaO per 100 cc. of juice where calcium saccharate is used as the liming reagent, as in factories employing the Steffen process for beet sugar manufacture. Where milk of lime is used as the liming reagent the saturation point is somewhat lower, because milk of lime is less soluble than calcium saccharate. It will be understood, of course, that the alkalinity of the juice at the saturation point varies somewhat with different juices and with different liming reagents, and also that the alkalinity corresponding to the lower limit of the critical foaming range varies with different juices and different liming reagents. The approximate limits of the critical foaming range, however, can be readily determined in each case by sample tests, and no difficulty is encountered in thus selecting alkalinity values which lie outside of the foaming range but near its limits.

From the foregoing it will be understood that the process of this invention must be carried out as a continuous carbonation process. tice several tanks (usually four) are connected together in series and utilized for continuous treatment of the juice. The juice is sup-plied continuously to the first of these tanks, preferably after having been heated to a temperature between 80 and 90 C. and subjected to a continuous pre-defecation process, such as claimed in the aforesaid United States Letters Patent, to establish an alkalinity somewhat in excess of the optimum alkalinity for the flocculation of colloidal impurities.

Liming reagent is continuously added to the juice supply for the first carbonation tank so that the juice in this tank will be saturated with dissolved liming reagent and will contain an excess of undissolved liming reagent. For example, about 75% of the liming reagent employed in the main carbonation process may be incorporated with the juice in the first tank. The remaining part of the liming reagent is preferably divided between the third and fourth tanks of the system and added continuously to the juice streams entering those tanks.

The treatment with carbon dioxide gas is begun in the second tank, continued in the third tank and finished in the fourth tank, a continuous stream of carbon dioxide being introduced into each of these tanks.

In one embodiment of the present invention the heavily limed juice from the first tank passes continuously into and through the second tank and is there treated continuously with carbon dioxide gas at such a rate that the juice in the second tank is always maintained at an alkalinity above the critical foaming range; for example, the juice in the second tank is held at or about the point of saturation with liming reagent. In the case of calcium saccharate, the alkalinity at this saturation point is about 0.40 to 0.50 gram CaO per 100 cc. of juice. The juice so treated in In practhe second tank then passes continuously into a third tank, where carbon dioxide is introduced at such a rate that the alkalinity of the juice in the third tank is maintained at a point just below the critical foaming range; for example, the juice in the third tank may be held at an alkalinity of about 0.11 to 0.20 gram CaO per 100 cc. The juice then passes from the third tank into a fourth tank, where carbon dioxide is introduced at such a rate that the alkalinity of the juice is lowered to the desired end point, for example, to about 0.06 to 0.08 gram CaO per 100 cc.

According to a, second embodiment of the invention, the juice entering the second tank with an excess of liming reagent is treated continuously with carbon dioxide gas at such a rate that the alkalinity of juice in the second tank is always maintained at a point below the critical foaming range, for example, at a point between 0.11 and 0.20 gram CaO per 100 cc. The juice from the second tank then passes successively through the third and fourth tanks, where continuous streams of carbon dioxide are introduced in such manner as to reduce the alkalinity to the desired end point in these two stages.

In either embodiment. carbon dioxide is supplied to the third and fourth tanks in sufficient volume to maintain the desired conditions of alkalinity in such tanks, having regard in each instance to the alkalinity of the juice in the tank next preceding and the rate at which liming reagent is added to the juice stream between tanks.

The aforesaid second embodiment of our invention is the preferred embodiment because control of the process is easier and more positive, there being only one danger point-the lower limit of the foaming range-to be avoided instead of two.

The accompanying drawing shows diagrammatically an installation of apparatus suitable for use in the practice of our invention.

Four tanks for continuous carbonation are designated by numbers I, 2, 3 and 4, respectively.

" Juice entering the process is introduced near the bottom of tank I. Tanks I, 2, 3 and 4 are connected in series, the connections being such that the juice in each tank overflows at an established level and passes into the lower part of the next tank. Liming reagent is supplied continuously to a distributor D, from which continuous streams of liming reagent may be supplied at the desired rates into the juice streams entering tanks I, 3 and 4, respectively. Carbon dioxide gas is supplied continuously to gas distributors located in the lower portions of tanks 2, 3 and l, respectively. The finished carbonated juice from tank 4 is passed onward for filtration.

In practice, our invention has been found susceptible to smooth and uniform operation, and excessive foaming and the difiiculties resulting therefrom are effectively eliminated. While some foaming usually occurs during carbonation, the foam which forms during the practice of our process consists of large, relatively unstable bubbles which offer no substantial resistance to flow and do not noticeably reduce the gas absorption efiiciency of the juice. Thus maximum capacities are obtained from the carbonation station, and the use of oil or other anti-foam reagents is eliminated.

Although we have mentioned specifically the alkalinization of sugar juice with lime or calcium saccharate, it will be understood that these conventional liming reagents might be substituted by equivalent reagents such as barium hydroxide or strontium hydroxide. The term liming reagent is used in the present specification and claims as including any of these equivalent reagents. Alkalinity values are expressed in terms of grams of CaO per 100 cc. of juice, in accordance with conventional practice in the art.

It will be apparent to those skilled in the art that our invention may be applied in practice without restriction to the illustrative details disclosed hereinabove, and we therefore desire that our invention be accorded a scope fully commensurate with its novel contributions to the art, as limited only by the fair requirements of the appended claims.

We claim:

1. A carbonation process for purifying beet sugar juice which comprises heating the juice, adding liming reagent thereto in an amount exceeding that required to saturate the juice with liming reagent, passing the so limed juice in a continuous stream through a predetermined path, introducing a plurality of continuous streams of liming reagent and carbon dioxide gas into the juice stream at spaced points in said path and thoroughly mixing said streams with the juice, controlling the introduction of said streams of liming reagent and carbon dioxide so that the juice in successive stages of lower alkafactory for filtration, and controlling the volume of said carbon dioxide streams so that the juice possesses an alkalinity outside of its active foaming range at each of said stages, said active foaming range lying above said end point between a point slightly below the point of saturation with liming reagent and a point, depending on the quality of the juice, not exceeding about 0.20 gram CaO per 100 cc. of juice.

2. A carbonation process for purifying beet sugar juice which comprises passing a continuous stream of juice to be purified, while heated to temperature suitable for hot carbonation, through a predetermined path, in one zone of said path continuously incorporating with said juice stream liming reagent in an amount exceeding that required to saturate the juice, thereafter continuously carbonating the juice stream in further zones of said path so as to lower the alkalinity of the juice in stages and attain an end point suitable for filtration corresponding to an alkalinity of about 0.06 to 0.08 grams CaO per 100 cc. of juice, and effecting said carbonation of the juice stream at such a rate that each of said alkalinity lies outside reagent and a point, depending on the quality of the juice, not exceeding about 0.20 gram CaO per 100 cc. of juice.

3. A carbonation process for purifying beet sugar juice which comprises passing a continuous stream of the juice while heated to a temperature suitable for hot carbonation, through a predetermined path, in one zone of said path incorporating with the juice stream liming reagent in an amount exceeding that required to saturate the juice, in a second zone of said path continuously carbonating the so limed juice stream at a rate suilicient to maintain its alkalinity at a point, below its active foaming range, equivalent to about 0.11 to 0.20 gram CaO per 100 cc. of' juice, and thereafter continuously carbonating the juice stream to an end point suitable for filtration.

4. A carbonation process for purifying beet sugar juice which comprises passing a continuous stream of the juice, heated to a temperature suitable for hot carbonation, through a predetermined path, in one zone of said path incorporating in the juice stream liming reagent in an amount exceeding that required to saturate the juice, in a second zone of said path continuously carbonating the so limed juice stream at a rate suflicient to precipitate the excess of said liming reagent and still leave the juice at about the point of saturation with liming reagent, in a third zone of said path continuously carbonating the juice stream at a rate sufiicient to maintain its alkalinity equivalent to about 0.11 to 0.20 gram of CaO per 100 cc. of juice, and in a fourth zone of said path continuously carbonating the juice stream to an end point suitable for filtration.

5. A carbonation process for purifying beet sugar juice which comprises passing a continuous stream of the juice, at a temperature between about and 0., through a predetermined of said path incorporating in liming reagent in an amount exceeding that required to saturate the juice, in a second zone of said path continuously carbonating the so limed juice stream at a rate suflicient to precipitate the excess of said liming reagent and still leave the juice at about the point of saturation with said liming reagent, introducing a continuous stream of liming reagent into the juice stream passing from said second zone into a third zone of said path, continuously carbonating said juice stream in said third zone at a rate suflicient to keep its alkalinity in said third zone equivalent to about 0.11 to 0.20 gram of CaO per cc. of juice, introducing a continuous stream of liming reagent into the juice stream passing from said third zone into a fourth zone of said path, and continuously carbonating said juice stream in said fourth zone to an alkalinity of about 0.06 to 0.08 gram of CaO per 100 cc. of juice.

6. A carbonation process for purifying beet sugar juice which comprises passing the juice to be carbonated, at a temperature between about 80 and 90 0., in a continuous stream into a first tank, combining with the juice entering said first tank a continuous stream of liming reagent of such volume that the juice in said first tank is tank at about 0.11 to 0.20 gram CaO per 100 cc., continuously passing juice from said second tank into a third tank, combining with such juice entering said third tank a small continuous stream of liming reagent, treating the juice in said third tank with a continuous stream of carbon dioxide so regulated as to keep the alkalinity of the juice in said third tank at a point intermediate the desired end point of carbonation and the alkalinity of juice in said second tank, continuously passing juice from said third tank into a fourth tank, combining with such juice entering said fourth tank a small continuous stream of liming reagent, treating the juice in said fourth tank with a continuous stream of carbon dioxide so regulated as to keep the alkalinity of juice in said fourth tank at an end point of about 0.06 to 0.08 gram CaO per 100 cc. of juice, and continuously passing carbonated juice from said fourth tank on-ward for filtration and removal of precipitated i-rn purities.

7. A carbonation process for purifying beet sugar juice which comprises passing pre-limed juice to be carbonated, at a temperature between about 80 and 90 C., in a continuous stream through a predetermined path, combining with the juice stream entering said path a continuous stream of calcium 'saccharate solution constituting :a major part of the total flow of such solu- 111011 to be added to the .juice during the main carbonation process, continuously supplying carbon 

